Hive视图<转>

Hive 0.6版本及以上支持视图
Hive View具有以下特点：
1. View是逻辑存在，Hive暂不支持物化视图(1.0.3)
2. View只读，不支持LOAD/INSERT/ALTER。需要改变View定义，可以是用Alter View
3. View内可能包含ORDER BY/LIMIT语句，假如一个针对view的查询也包含这些语句， 则view中的语句优先级高。例如，定义view数据为limit 10， 针对view的查询limit 20，则最多返回10条数据。
4. Hive支持迭代视图

创建View

 CREATE VIEW [IF NOT EXISTS] view_name [(column_name [COMMENT column_comment], ...) ]
 [COMMENT view_comment]
 [TBLPROPERTIES (property_name = property_value, ...)]
 AS SELECT ...

删除view

 DROP VIEW [IF EXISTS] view_name

修改view

 ALTER VIEW view_name SET TBLPROPERTIES table_properties

 table_properties:
   : (property_name = property_value, property_name = property_value, ...)

实例：

 hive> desc student;
 OK
 id      int
 name    string
 academy string
 class   string
 Time taken: 0.146 seconds
 hive> create view student_view (id, name_length) as  select id, length(name) from student;
 OK
 Time taken: 0.424 seconds
 hive> desc student_view;
 OK
 id      int
 name_length     int
 Time taken: 0.071 secondshive> select * from student;
 Total MapReduce jobs = 1
 ......
 Total MapReduce CPU Time Spent: 680 msec
 1       20      computer        034
 2       21      computer        034
 3       19      computer        034
 4       18      computer        034
 5       22      computer        034
 6       23      computer        034
 7       25      computer        034
 1       20      physics 034
 2       21      physics 034
 3       19      physics 034
 4       18      physics 034
 5       22      physics 034
 6       23      physics 034
 7       25      physics 034Time taken: 0.176 seconds
 hive> select * from student_view;
 Total MapReduce jobs = 1
 ......
 Total MapReduce CPU Time Spent: 680 msec
 OK
 1       2
 2       2
 3       2
 4       2
 5       2
 6       2
 7       2
 1       2
 2       2
 3       2
 4       2
 5       2
 6       2
 7       2
 Time taken: 20.592 secondshive> create view student_view_view(id)
     > as
     > select id from student_view;
 OK
 Time taken: 0.215 seconds
 hive> select * from student_view_view;
 Total MapReduce jobs = 1
 .....
 Total MapReduce CPU Time Spent: 790 msec
 OK
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